1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor laser, a semiconductor laser, an optical pickup, an optical disk device, a method of manufacturing a semiconductor device, and a method of growing a nitride type Group III-V compound semiconductor layer, and is preferable when applied, for example, to a ridge stripe type semiconductor laser having an end face window structure using a nitride type Group III-V compound semiconductor, and an optical pickup and an optical disk device which use the semiconductor laser as or in a light source.
2. Description of the Related Art
In order to increase the maximum optical output of a semiconductor laser, it may inevitably be necessary to introduce an end face window structure in which an end face of a resonator is provided with a window transparent to the light coming from an active layer.
In a GaInP red light emitting semiconductor laser according to the related art, a method has been effective in which after the growth of a semiconductor layer forming a laser structure, Zn atoms are diffused into the semiconductor layer in the vicinity of a part to be a resonator end face so as to locally increase the band gap energy, thereby forming an end face window structure (refer to, for example, Japanese Patent Laid-open No. 2005-45009).
On the other hand, in recent years, semiconductor lasers based on a nitride type Group III-V compound semiconductor have been used as light sources in high-density optical disk devices and the like. Most of the nitride type Group III-V compound semiconductors are materials which are thermally and mechanically stabler than GaInP semiconductors. Therefore, in the semiconductor laser based on a nitride type Group III-V compound semiconductor, it is difficult to achieve formation of an end face window structure by diffusion of different kinds of atoms and wet etching, which have been effective in the case of the GaInP red light emitting semiconductor laser.
In view of this, with regard to the semiconductor lasers based on a nitride type Group III-V compound semiconductor, a variety of methods for forming an end face window structure have been proposed and put to experiment. Now, methods of forming an end face window structure which have been proposed will be described as follows.
It has been proposed to form an end face window structure through increasing the band gap energy in the vicinity of an end face of a resonator by utilizing an In elimination process caused by irradiation with laser light or exposure to a H2 plasma after the formation of a laser bar by cleavage (refer to, for example, Japanese Patent Laid-open No. 2006-147814 and Japanese Patent Laid-open No. 2006-147815). However, for carrying out these methods, a high-vacuum chamber equipment may be needed, leading to a large-scale plant and equipment investment. Besides, processing the resonator end face after cleavage will generally leave a problem as to productivity.
Many proposals have been made regarding a method in which after a semiconductor layer for forming a laser structure is epitaxially grown on a substrate, a part of the semiconductor layer which is to be a resonator end face is dug by reactive ion etching (RIE), and a nitride type Group III-V compound semiconductor layer with a high band gap energy is again epitaxially grown in the dug area (refer to, for example, Japanese Patent Laid-open No. 2004-134555, Japanese Patent Laid-open No. 2003-60298, International Publication No. 03/036771 pamphlet, and Japanese Patent Laid-open No. 2002-204036). According to this method, however, a surface level would be formed at the surface dug by RIE, leading to the fear that light absorption and local heat generation may occur at the time of laser operation.
As another example, a method has been proposed in which a semiconductor layer for forming a laser structure is epitaxially grown on a substrate provided with a geometric step by RIE or insulating film deposition, whereby an end face window structure is formed (refer to, for example, Japanese Patent Laid-open No. 2005-191588, Japanese Patent Laid-open No. 2005-294394, Japanese Patent Laid-open No. 2003-198057, and Japanese Patent Laid-open No. 2000-196188). This method aims at a phenomenon in which a clad layer higher in band gap energy than an active layer functions as an end face window structure, in the traveling direction of laser light. A typical example of this is shown in FIG. 42. As shown in FIG. 42, in this semiconductor laser, one principal surface of a substrate 101 is patterned by RIE to provide a recess 101a, then an n-type semiconductor layer 102, an active layer 103 and a p-type semiconductor layer 104 are sequentially grown over the recess 101a, and thereafter a p-side electrode 105, an isolation electrode 106 and a pad electrode 107 are formed over the p-type semiconductor layer 104. In other words, steep geometric steps are generated in the n-type semiconductor layer 102, the active layer 103 and the p-type semiconductor layer 104 due to the presence of the recess 101a in the substrate 101, so that an optical waveguide loss would be generated in the vicinity of the steps. Besides, transparency acquired by gap widening in the active layer 103 in the vicinity of the resonator end face is not intended and, therefore, the semiconductor structure may fail to function as an effective end face structure.